I'll answer these questions using this candle flame as an example.

This candle has a wick that's embedded in wax. The wick burns

slowly, but it's mainly the wax that's the fuel.

Let's look at it more closely. The wax is largely made up of carbon

and hydrogen atoms bonded together into large hydrocarbon molecules.

To start the fire going we apply heat. When we do, that causes the

molecules to move around vigourously, breaking the wax molecules

into individual carbon and hydrogen atoms. These individual atoms are no

longer a part of a solid structure but are now a gas. This process is

called pyrolysis.

Next, these atoms, still moving around vigourously due

to the heat, collide with oxygen atoms in the air. When they do,

they give off bluish light. This is the bluish color you see at the

base of the flame. This process is called chemiluminescence.

The oxygen atoms also bond with the hydrogen and carbon atoms

to form new molecules, such as water, with two hydrogens and an oxygen,

and carbon dioxide, with one carbon and two oxygens.

When they do bond, energy is released in the form of more heat.

This is called oxidation.

In some fires, such as candle fires, there are a lot of extra carbon atoms left over.

These carbon atoms combine together to form

soot. The heat heats up the soot and when it reaches

certain temperature ranges it glows with visible light,

and with a candle flame, mostly yellowish light.

At the tip of the yellowish flame the temperature reaches around

1200 degrees celsius or 2200 fahrenheit.

This process is called incandescence.

As to why a flame has the shape it does, that's because hot air

rises "up"ward. And in this case it's the air surrounding the flame

that's being heated and rises up. When it does, cool air rushes in to

replace it and that cool air also heats up and rises. This continulal

cycle is called convection and it's this that corrals the flame into

its teardrop shape.

As an interesting side-note, heat rises like this only in a gravity

environment. When a flame burns in an environment with little or no

gravity, as was done in experiments in the space shuttle, the flame

is more spherical in shape since there is no "up".

Well, thanks for watching!

Check out my youtube channel, rimstarorg, for more videos like this.

That includes one explaining hot, neutral and ground and why our

power outlets have such strange shapes. One on how nuclear fusion

works in the sun. And one about how fast electrons and electricity

move in a wire.

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